Altostratus belong to the Middle Cloud group (2000-7000m up). An altostratus cloud usually covers the whole sky and has a gray or blue-gray appearance. The sun or moon may shine through an altostratus cloud, but will appear watery or fuzzy.

An altostratus cloud usually forms ahead of storms with continuous rain or snow. Occasionally, rain will fall from an altostratus cloud. If the rain hits the ground, then the cloud becomes classified as a nimbostratus cloud.